1. Field of the Invention
The present invention relates to a printing apparatus for performing colorimetry of a color pattern formed on a sheet and a reading method in a printing apparatus.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2008-254221 discuses an ink jet printer including a colorimetric apparatus. This colorimetric apparatus performs colorimetry of a printed color pattern for color calibration and, based on colorimetric data, adjusts colors of color images to be subsequently printed, thus reproducing desired colors. The printer prints color patches as a color pattern for color calibration, and then the colorimetric apparatus performs colorimetry of the color patches with a colorimetric sensor moving in the sheet width direction.
The colorimetric apparatus discussed in Japanese Patent Application Laid-Open No. 2008-254221 includes a printing unit, a reading unit, and a drying unit disposed in this order from upstream to downstream of the sheet conveyance path. The printing unit forms color patches in a sheet area and sends the sheet area to the drying unit. The drying unit dries the sheet area and sends it back to the printing unit. Then, the reading unit reads the color patches.
The colorimetric apparatus discussed in Japanese Patent Application Laid-Open No. 2008-254221 reads the color patches only once. Specifically, the colorimetric apparatus takes into consideration one row of color patches, which can be read in one scan by the colorimetric sensor. Actually, however, forming a greater number of colors in a plurality of rows of color patches enables performing more accurate color calibration. When such color patches formed in a plurality of rows are read, a reading time increases since the number of scans increases. To practically apply the colorimetric apparatus, preventing an increase in total time of inspection, i.e., improving the total throughput, becomes an issue.
When performing sheet colorimetry, the colorimetric apparatus discussed in Japanese Patent Application Laid-Open No. 2008-254221 rotatably shifts a presser plate, which is regularly raised, to press a sheet. Subsequently, a carriage on which the colorimetric sensor is mounted moves to the presser plate and then reads the color patches while moving thereabove. With this configuration, while the carriage exists above the presser plate, it is not possible to rotate the presser plate to retract the carriage. Specifically, to release the pressing by the presser plate to move the sheet, it is necessary to retract the carriage to the outside of the presser plate. The carriage reads the color patches only in the forward path and returns to the home position in the backward path (back feed). Before the carriage completes back feed (backward path) and retracts from above the presser plate to the outside, a following sheet cannot start being moved. This means that the time loss required for back feed disturbs the improvement in reading throughput. In particular, this issue will become distinct when sequentially reading a number of test patterns through repetitive carriage operations.
With the colorimetric apparatus discussed in Japanese Patent Application Laid-Open No. 2008-254221, when the wheel of the carriage runs upon the presser plate, the wheel passes the level difference for the thickness of the presser plate and the impact is transmitted to the carriage. Repetitively applying this impact to the carriage may cause degradation in the attachment accuracy of the colorimetric sensor or a failure of the colorimetric sensor. When the carriage is retracted to the outside of the presser plate, the wheel of the carriage travels on the sheet without the presser plate. Accordingly, when the sheet has a pattern or image printed thereon, the pattern or image may be damaged by the track of the wheel. Each of these factors may cause degradation in reading accuracy.